The experiments are directed at identifying the cellular transport processes involved in intracellular pH (pHi) regulation in the principal and intercalated cells of the cortical and outer medullary collecting tubule of the rabbit. I will use the isolated perfusion tubule preparation, a recently developed videomicrofluorometer and the pH probe 1,4DHPN to measure pHi in individual cells. First, the transport processes involved in pHi regulation in both cell types will be determined. Second, the coupling of energy metabolism to work output, and the substrate specifity of this process will be assessed by measuring the fluorescence of NADH in individual cells. The results will increase the understanding of bicarbonate reabsorption and secretion in the collecting tubule which will be important in understanding various pathophysiologic states of acid-base homeostasis which affect the distal nephron.